Conventionally, a technology for performing channel estimation with known signals called pilot signals and demodulating received data based on a result of the channel estimation has been introduced. Furthermore, for a cellular wireless communication system, a technology for using a different pilot signal for each base station has been proposed to prevent the possibility that received data may not normally be demodulated due to interference between pilot signals transmitted from adjacent base stations.
Such a technology is disclosed in for example Japanese Laid-open Patent Publication No. 2007-300316.
However, in the above-mentioned conventional cellular wireless communication system, because an identical pilot signal is used in each cell, there is a problem in that data transmitted and received by a mobile station may relatively easily be demodulated by other mobile stations located in the same cell.
When highly-confidential information is wirelessly transmitted and received, it may be possible to perform communication after performing encryption to prevent information leakage. However, the encryption is performed in a higher layer than a physical layer, and, in the physical layer at the lower level, a process for demodulating the encrypted data and transmitting the data with insertion of a pilot signal is performed. Therefore, the pilot signal itself is not encrypted and a third-party mobile station located in the same cell can demodulate the encrypted data, so that the information may be deciphered afterward.